1. Field
The presently disclosed embodiment relates to a cleaning fluid and a cleaning method. More particularly, the presently disclosed embodiment relates to, in an inkjet printer which ejects aqueous inkjet ink containing pigment and alkali-soluble resin having an acid base in a molecule, a cleaning fluid and a cleaning method for cleaning a site to which the aqueous inkjet ink being ejected adheres.
2. Brief Description of Related Developments
Inkjet type printing is a technique which employs an inkjet printer to eject an ink droplet from an extremely fine nozzle to a printing substrate and form a colored image, such as letters and patterns. Inkjet type printing does not require a plate making process and can perform high-quality printing with a quite simple configuration of apparatus. Therefore, inkjet type printing has many advantages that are hard to get with other techniques. Inkjet printers employing inkjet type printing have been very popular in the field of personal use, such as individual use or use at home.
On the other hand, in industrial use, where an incompatibly larger quantity of printed matter than in personal use is produced, various kinds of performance characteristics are additionally required. First, high speed printability is essential to improve producibility. Also, the printed matter is wound or superimposed soon after being printed. Thus, the printed matter needs to be dried sufficiently so that the printed surface is not contaminated and do not stain the back side of printing paper which contacts the printed surface. It is also important that cost of the printed matter is low. Especially, printed matter in industrial use, even without employing dedicated paper as used in personal use, must achieve sufficient print quality. Of course, ink for producing printed matter of industrial use must have performance characteristics of ink required essentially for inkjet type printing, too. Major examples of such performance characteristics include preservation stability with time, ejection reliability allowing stable ejection without causing nozzle clogging, flying capacity for a droplet to impact exactly on a target position, water resistance and rubfastness of print material, and the like.
As stated above, for employing inkjet type printing in industrial use, many of performance characteristics of ink has yet to be improved. However, considering the recent trend toward multi-kind and small lot of print material, and the like in the printing industry, inkjet type printing, if improved in print speed and print quality on low-cost printing paper, is worth employing, even in competition with other types of printing. Therefore, in an effort to employ inkjet type printing in industrial use, technique achieving high speed printing and decorative printing on low-cost printing paper has been actively developed in terms of a printer, ink, printing method, and the like.
First, in order to achieve high speed printing, a lot of ink droplets have to be ejected onto a predetermined position in a shorter time. Then, attempts have been made to increase nozzles ejecting ink droplets. Specifically, a method of single-pass printing using a fixed line head has been developed. However, inkjet type printing is mechanically restricted that droplets cannot be ejected until filling of ink into a nozzle is finished. Therefore, in inkjet type printing a time lag occurs by the next ejection at least for a duration as long as ink is filled into a nozzle. Therefore, for faster printing, improving performance of ink itself is considered so that filling of ink is finished more quickly. For example, there have been attempts to lower ink viscosity.
Next, in order to achieve cost reduction, it has been considered to employ uncoated paper, such as cheap plain paper and regular offset paper, which are not specially processed to enhance print suitability for printing paper. However, fibers of such printing paper are sparse and a liquid component of ink tends to permeate deeply into the paper (fibers). This tendency becomes evident when low-viscosity ink is used. If, with a liquid component of ink, a coloring component is permeated into paper, density and clearness of a printed image are reduced. When a liquid component of ink spreads along fibers on a surface of paper, bleeding occurs. Either case impairs print quality of printed matter. Therefore, when plain paper and regular offset paper are used, measures are required to prevent occurring of reduced density and clearness and of bleeding.
The problem of lowering ink viscosity and inhibiting permeation of a coloring component into paper at the same time and a problem of improving drying property and ejection reliability at the same time respectively cannot be improved without altering physical properties of ink in the opposite direction. Thus, it is difficult to improve these conflicting problems at the same time.
Then, in aqueous ink, in order to lower ink viscosity and achieve a quick drying property and inhibition of permeation of a coloring component into paper, a method of desorbing an aqueous medium from the system quickly when the ink impacts on a paper surface has been considered. For example, one is a technique introducing a highly hydrophobic portion of a long chain alkyl group, an aromatic ring, and the like into a molecule as binder resin and using alkali-soluble resin designed to have a low acid value in the smallest possible amount so that low viscosity of the ink is maintained while increasing a concentration of pigment as high as possible. Furthermore, regarding preservation stability and ejection reliability which tend to be reduced due to this technique, a technique has been considered, in which this binder resin is deposited on a surface of pigment and coats the surface of the pigment for maintaining the preservation stability and ejection reliability.
However, in this method, once ink is dried and solidified, it is hard to redissolve. Therefore, in an inkjet printer and the like which has been left for long time without ejecting ink, a dry film of the ink is formed on a head (near a nozzle tip) or in a nozzle. The dry film tends to be a cause of curved flight of ink and nozzle clogging.
Then, a technique employing ink cleaning fluid to remove a dry film of ink accumulated in a head or a nozzle has been suggested. For example, Japanese Patent Document No. 2009-155424A discloses a method employing a two-component cleaning fluid for inkjet head which consists of two kinds of cleaning water containing different surfactants. Japanese Patent Document No. 2000-127419A discloses a nozzle cleaning fluid for an inkjet recording head which contains surfactant, a basic compound, and water and has a pH of 9 or higher. Japanese Patent Document No. 2012-067152A discloses a method of cleaning a hard surface with aqueous detergent containing alkali chemical, alkylamine oxide, and particular organic solvent.